The Twist, which is either hilarious or horrifying, is that instead of zombies, the infected victims turn into rabid living amusement park mascots.
The series of course, has a stab at this in chapter 39.The Nightshift in Dawn Tsumetai Te, which take over a host's body and slowly eat it from the inside out.They latch on to the heads of cells, causing the equivalent of a Zombie Apocalypse. Cells at Work!, being an Anthropomorphic Personification of the cells of the body, has quite possibly the most literal depiction of this trope - viruses, the most fundamentally basic parasite.
